Light-induced photoreductants can be employed to excite triplet state oxygen to singlet state oxygen which can be employed in the formation of hydroperoxide sites which functionalize the initiation of polymerization reactions.
Singlet state oxygen can be reacted with unsaturated polymeric rubbers, such as diene rubber compounds, to form the corresponding hydroperoxide functionalized rubbers. The hydroperoxide functionalized sites on the rubber backbone provide reactive sites which enhance the grafting efficiency in the reaction of the rubbery polymer with the monomers which form pendant groups on polymeric backbones. The grafting efficiency for a particular monomer-polymer system is thus a function of the number of peroxide groups formed on each molecule of the rubbery polymer. All things being equal, the number of pendant groups formed on the polymer backbone increases with the efficiency of the photoreductant in exciting the triplet state oxygen to a singlet state.
Suitable photoreductant formulations for the production of hydroperoxide derivatives of rubber by the reduction of triplet state oxygen to singlet state oxygen are disclosed in U.S. Pat. No. 5,075,347. As disclosed there, various photosensitizing agents such as methylene blue, rose bengal, and others are dissolved in a solution of a rubbery polymer through the use of an alcohol-based solubilizer such as methanol, which enhances the solubility of the photosensitizing agent in the rubber solution. The rubbery solution containing the photosynthesizing agent is oxygenated and then subjected to irradiation with light having a wavelength in the 300-800 angstrom region to convert triplet oxygen to singlet oxygen for use in the polymerization of the rubber-containing solution.